Similar to a situation I just had, though a bit different. I had a failing queen in a hive and requeened in December. Folks at the bee club said I'd probably lose the hive. Sorry, not happening. I added 1 brood and nurse bees and shrunk it to a nuc. Temps after the changes had been in 70s and 80s so I wasn't too concerned about temperature at the time. Looking at Sacramento weather, your temps are running close to ours right now. On the recommendation of others here, I got a terrarium heater for it. It's a 16 W "Reptitherm" under tank heater. It was $35 at Petsmart. Size was perfect for nuc. Nuc has SBB and I put it under the hive and set hive on plywood. I ran a test with the 8W and it didn't make much difference in an unpopulated nuc. I switched it for the 16W one, and it kept temps in the low 70s in the hive on a 45 degree night, so I knew it won't cook bees. Then I rotated out the 8 W one with the 16 W one and returned the 8W. I think it's just enough to keep the edge off based on our temp spread here.